P0171 System Too Lean (Bank 1) = Vacuum Leak??

[sunfire]

The car (see my sig) was driven 5 minutes so it was warm when the data was collected.

When my LTFT increases with RPM does that indicate a vacuum leak? Ideally, LTFT should be 0.


Code:


CAR PARKED



RPM STFT LTFT

700idle 0.7-2.3 5.4

1K -1 6.2

2K 2.3 6.2-6.5

3K 2.7 7.8-9

4K 1.3-1.5 12.5





DRIVING



STFT LTFT

2K -3 11.7-12.5


I'm going to collect better data points next time I go out.

 

[sunfire]

I just want make sure it is air related and not a problem with fuel pressure or the injectors. I don't want to start tearing apart the car without analyzing data first.

 

[CharBaby]

Usually a A/F Sensor or O2 Sensor.

 

[wirelessF]

Intake gaskets, googled it and looks like it s a common issue. Try confirming this by spraying carb cleaner around the lower intake manifold area and the idle increases/jumps up.

 

[mikered30]

Change the intake manifold gasket with the new revised orange gasket and it will fix your problem. TN has the DIY in the 9th gen section, takes about an hour.

 

[yonyon]

Your LTFT is going up as you increase engine speed and load. It is not a vacuum leak. Start by checking your MAF for buildup of gunk, poop, or other nastiness on the wires that the air flows over. If that isn't it, check fuel pressure next.

 

[mikered30]

TSB

 

[yonyon]

Originally Posted By: sunfire
I just want make sure it is air related and not a problem with fuel pressure or the injectors. I don't want to start tearing apart the car without analyzing data first.


When you increase metered airflow rate (look for MAF in grams per second on your scan tool) by increasing engine speed you are not also proportionally increasing airflow through any vacuum leak(s) so the %error in measurement decreases -> total fuel trim (long + short) goes down closer to zero.

What makes the fuel trim go up with increased airflow? Typically two things:
-inability of the hardware to measure airflow at higher speeds (dirty MAF sensor)
-inability of the hardware to deliver fuel at higher volumes (clogged filter, pinched fuel line, that sort of thing)

 

[sunfire]

Originally Posted By: wirelessF
Intake gaskets, googled it and looks like it s a common issue. Try confirming this by spraying carb cleaner around the lower intake manifold area and the idle increases/jumps up.


Originally Posted By: mikered30
Change the intake manifold gasket with the new revised orange gasket and it will fix your problem. TN has the DIY in the 9th gen section, takes about an hour.


The intake manifold gasket was the first on my list of things to test. I'm more interested in collecting and interpreting the data than fixing the problem immediately. This condition has existed for a while. I'm going to collect a little more data maybe try plotting it.

RPM vs LTFT
MAF vs LTFT

If the conditions are right I'm going to spray the intake manifold.

 

[sunfire]

Highway driving probably about 1-2 minute capture.

 

[yonyon]

Your points are a bit more scattered than I'd expect - could possibly be an AFR sensor going bad but I still thing it's worth taking 10 minutes to check/clean the MAF. If you collect any more data, keep in mind that total trim can give a clearer picture than long trim.

 

[Vikas]

All I am seeing is that somebody got a new toy and is just playing with it Was there a real question here somewhere?

 

[yonyon]

The very thread title is a question. sunfire wants to know if the P0171 code in his Corolla is caused by a vacuum leak.

 

[sunfire]

Originally Posted By: Vikas
All I am seeing is that somebody got a new toy and is just playing with it Was there a real question here somewhere?


I've had the code reader for a long time. In fact, it's archaic compared to the Torque Pro android app. P0171 has come up a few times. This time I'm determined fix it instead of just clearing it. But I want the data confirm the problem has been fixed. I need to have solid "before" data before I make changes to the car. I had trouble downloading the data from today's run.

Sorry this won't be a quick fix. It's so cold right now I can't even work on the car if I wanted to.

 

[MarkM66]

Originally Posted By: Vikas
All I am seeing is that somebody got a new toy and is just playing with it Was there a real question here somewhere?


Exactly what I was thinking. Would of took less time to just change the intake gasket...

 

[Vikas]

yonyon has already honed on it. You need to add LT+ST and then look at the numbers. Your total trim seems to be constant rather varying with the engine load/rpm. I believe his suggestion to clean MAF sensor make sense. You can also add MAF readings to monitor and compare them to known good MAF readings for this vehicle (that might be tough).